1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems for detecting battery disconnection from a device, thereby allowing the device to be shut down in a controlled manner.
2. Discussion of the Background
In order to shut down in a controlled manner upon an intentional or accidental disconnection of a battery, a device (e.g., a mobile terminal) needs to promptly receive an indication that the battery is physically disconnected. Shutting down in a controlled manner is important for preserving data integrity and security. For example, when an accidental disconnection of the battery from the mobile terminal occurs, it is important that any ongoing data exchange concludes in an orderly manner.
A good battery presence detection system should have some or all of the following properties: a sufficiently short response time (e.g., typically less than 500 μs) in order to allow adequate time for the mobile terminal to shut down in a controlled manner, cost efficient reuse of existing hardware in the device, usable with batteries of various types, use as little power as possible in order to avoid using up the stored energy in the battery, useable long enough after the battery is disconnected to provide the indication needed to shut down the mobile terminal in a controlled manner, and be fault tolerant, so as not to indicate that minor glitches or noise are battery disconnections.
A typical battery 100, as illustrated in FIG. 1, has physical connectors 102 that are connectable to corresponding physical connectors of a corresponding, battery-powered device (e.g., a mobile terminal). At least three lines, a battery presence detection line (BDET) 104, a battery ground line (GND) 106 and a battery cell voltage line (VBAT) 108 are typically present in the battery and can be connected to the battery-powered device using the physical connectors 102.
The typical battery 100 usually includes a pull-down resistor 110 (RID) connected between the battery presence detection line 104 and the battery ground line 106. The pull-down resistor 110 has a value which typically is dependent on the battery type, but is typically not larger than 200 kΩ. In some batteries, the pull-down resistor 110 is temperature sensitive (or alternatively, the batteries include a resistive network including a temperature sensitive resistor) so that it can also be used to measure the temperature inside the battery 100. The battery 100 further includes a battery cell 112, which provides a battery voltage to the battery cell voltage line (VBAT) 108. The battery 100 also includes a safety integrated circuit 114 to protect the battery, for example, in case of overheating.
A common battery presence detection system includes a pull-up resistor in the battery-powered device, which forms a voltage division configuration in combination with the pull-down resistor 110 in the battery 100. A voltage division value is monitored by a continuous time comparator in the mobile terminal to determine the presence or absence of the battery 100.
The main drawback of the above-described battery presence detection system is that power is wasted by continuously feeding the voltage divider, the fed power being discharged to a ground line either via the pull-up resistor and the pull-down resistor when the battery is connected to the mobile terminal, or only via the pull-up resistor when the battery is not connected to the mobile terminal.
An alternative method used with the above-described battery presence detection system does not continuously provide power to the voltage divider, but instead turns on the battery presence detection system only temporarily. This alternative method has the disadvantage that the turning on/off of the detection system may be relatively slow, for example, allowing detection of whether battery is connected only about once per second. Such a long reaction time of the battery presence detection system is substantially larger than a desirable reaction time which assures a controlled shutdown of the mobile terminal. Additionally, this approach requires that some element of the detection system remain “awake” in order to turn on and off the rest of the detection system.
In recent years, manufacturers have produced smart batteries which allow digital communication with a mobile terminal, e.g., to provide information about a battery type, remaining capacity, etc. Typically, such digital communications have been transmitted over the battery presence detection line. However, the voltage present on this line due to the voltage divider circuit used for detecting the battery presence may interfere with the digital communications over the battery presence detection line. Adding a fourth contact/line to the battery interface to separate the digital communications associated with the smart battery from the battery presence detection is of course possible, but adds complexity and cost to the interface.
Accordingly, it would be desirable to provide battery presence detection systems and methods which overcome the afore-described drawbacks.